Update spi_api.c

Modified the spi_master_block_write() function yet again. SD related examples still read/erase/write the SD cards as expected and with these alterations the power consumption does not remain high after the SPI transaction has been finished. However i still only tested the SD functionality. Please test other SPI scenarios and different sensors as well to find out if this PR introduces unexpected bugs or not.

Changes:
- deleted the whole if (xfer.ui32NumBytes) condition as i did not find it logical (by that i mean xfer.ui32NumBytes was also true within the following else if (tx_length != rx_length){} block, so basically when the 2 buffers had different lengths an extra transfer has been done for nothing)
- removed the bool Rw = (rx_length >= tx_length) as the comparison >= has no sense anymore after if (tx_length == rx_length) on line 159.

Author: idea--list

targets/TARGET_Ambiq_Micro/TARGET_Apollo3/device/spi_api.c

@@ -151,57 +151,42 @@ int spi_master_block_write(spi_t *obj, const char *tx_buffer, int tx_length, cha
     MBED_ASSERT(obj);
 
     int chars_handled = 0;
+    uint32_t status = AM_HAL_STATUS_SUCCESS;
 
-    // perform a duplex xfer for the smaller of the two buffers
+    // always perform a duplex xfer
     xfer.eDirection = AM_HAL_IOM_FULLDUPLEX;
-    xfer.ui32NumBytes = (tx_length > rx_length) ? rx_length : tx_length;
-    xfer.pui32RxBuffer = (uint32_t *)rx_buffer;
-    xfer.pui32TxBuffer = (uint32_t *)tx_buffer;
-
-    if (xfer.ui32NumBytes) {
-        uint32_t status = am_hal_iom_spi_blocking_fullduplex(obj->spi.iom_obj.iom.handle, &xfer);
-        if (AM_HAL_STATUS_SUCCESS != status) {
-            return 0;
-        }
-        chars_handled += xfer.ui32NumBytes;
+
+    if (tx_length == rx_length) {
+        xfer.pui32RxBuffer = (uint32_t *)rx_buffer;
+        xfer.pui32TxBuffer = (uint32_t *)tx_buffer;
+        xfer.ui32NumBytes = tx_length;
+        status = am_hal_iom_spi_blocking_fullduplex(obj->spi.iom_obj.iom.handle, &xfer);
     }
 
     // handle difference between buffers
-    else if (tx_length != rx_length) {
-        bool Rw = (rx_length >= tx_length);
-
-        // set up common config
-        xfer.eDirection = (Rw) ? AM_HAL_IOM_RX : AM_HAL_IOM_TX;
-        xfer.ui32NumBytes = (Rw) ? (rx_length - tx_length) : (tx_length - rx_length);
-        xfer.pui32RxBuffer = (Rw) ? (uint32_t *)(rx_buffer + chars_handled) : NULL;
-        xfer.pui32TxBuffer = (Rw) ? NULL : (uint32_t *)(tx_buffer + chars_handled);
-
-        uint32_t status = AM_HAL_STATUS_SUCCESS;
-        if (!Rw || (write_fill == SPI_FILL_CHAR)) {
-            // when transmitting (w) or reading with a zero fill just use a simplex transfer
-            uint8_t fill[xfer.ui32NumBytes];
-            memset(fill, write_fill, xfer.ui32NumBytes);
-            xfer.eDirection = AM_HAL_IOM_FULLDUPLEX;
-            xfer.pui32RxBuffer = (uint32_t *)&fill;
-            uint32_t status = am_hal_iom_spi_blocking_fullduplex(obj->spi.iom_obj.iom.handle, &xfer);
-            if (AM_HAL_STATUS_SUCCESS != status) {
-                return chars_handled;
-            }
-            chars_handled += xfer.ui32NumBytes;
-        } else {
-            // when reading with a nonzero fill use a duplex transfer
-            uint8_t fill[xfer.ui32NumBytes];
-            memset(fill, write_fill, xfer.ui32NumBytes);
-            xfer.eDirection = AM_HAL_IOM_FULLDUPLEX;
-            xfer.pui32TxBuffer = (uint32_t *)&fill;
-            uint32_t status = am_hal_iom_spi_blocking_fullduplex(obj->spi.iom_obj.iom.handle, &xfer);
-            if (AM_HAL_STATUS_SUCCESS != status) {
-                return chars_handled;
-            }
-            chars_handled += xfer.ui32NumBytes;
-        }
+    else if (tx_length < rx_length) {
+        xfer.pui32RxBuffer = (uint32_t *)rx_buffer;
+        xfer.ui32NumBytes = rx_length - tx_length;
+        uint8_t fill[xfer.ui32NumBytes];
+        memset(fill, write_fill, xfer.ui32NumBytes);
+        xfer.pui32TxBuffer = (uint32_t *)&fill;
+        status = am_hal_iom_spi_blocking_fullduplex(obj->spi.iom_obj.iom.handle, &xfer);
+    }
+
+    else {
+        xfer.pui32TxBuffer = (uint32_t *)tx_buffer;
+        xfer.ui32NumBytes = tx_length - rx_length;
+        uint8_t fill[xfer.ui32NumBytes];
+        memset(fill, write_fill, xfer.ui32NumBytes);
+        xfer.pui32RxBuffer = (uint32_t *)&fill;
+        status = am_hal_iom_spi_blocking_fullduplex(obj->spi.iom_obj.iom.handle, &xfer);
+    }
+    
+    if (AM_HAL_STATUS_SUCCESS != status) {
+        return 0;
     }
 
+    chars_handled += xfer.ui32NumBytes;
     return chars_handled;
 }